For a recording method by means of an inkjet printer which is a typical method among various color recording methods, various methods of discharging ink have been developed, and any of them performs recording by generating ink droplets and depositing them onto various record-receiving materials (such as paper, film and cloth). This method has been rapidly prevailing lately and is expected to grow remarkably in the future because of such features as little noise generation due to no contact of a recording head with a record-receiving material and easiness in downsizing, speedup and colorization.
Conventionally, as an ink for a fountain pen or a felt pen and an ink for inkjet recording, a water-based ink dissolving a water-soluble dye in an aqueous medium has been used, and in these water-soluble inks, a water-soluble organic solvent is generally added to prevent ink from clogging at a pen tip or an inkjet nozzle. These conventional inks are required to provide a recorded image with sufficient density, not to clog at a pen tip or an inkjet nozzle, to dry quickly on a record-receiving material, to bleed less, to have good storage stability, and the like, and a formed image is required to have fastnesses such as water fastness, light fastness, and moisture fastness.
Meanwhile, when an image or character information on a color display of a computer is recorded in color by an inkjet printer, they are generally rendered using subtractive color mixing of four color inks, yellow (Y), magenta (M), cyan (C), and black (K). In order to reproduce, as faithfully as possible, their hues of an image by additive color mixing of red (R), green (G) and blue (B) on a CRT display and the like, with an image by subtractive color mixing, each of Y, M and C is desired to have such hue as close to each standard as possible and vividness. In addition, it is required that an ink composition to be used for it is stable in storage for a long period of time, and that an printed image has a high concentration and excellent fastnesses such as water fastness, light fastness and gas fastness.
Application of an inkjet printer is expanding in range from a compact printer for office to a large printer for industry, and fastnesses such as water fastness, moisture fastness, light fastness and gas fastness are required more than ever. Water fastness has been improved substantially by coating organic or inorganic fine particles which can adsorb coloring matter in ink, such as porous silica, cation-based polymer, aluminasol or special ceramics on the surface of paper, together with PVA resin and the like. Moisture fastness means durability against the phenomenon that coloring matter of dye in record-receiving material bleeds when colored record-receiving material is stored under a high humid atmosphere. Bleeding of coloring matter of dye leads to extremely deteriorating an image quality level especially in an image requiring high-definition image quality like photo tone, so it is important to cause as little bleeding as possible. Because any technique to improve light fastness greatly has not established yet and especially many types of coloring matter of magenta among 4 primary colors of Y, M, C and K are originally weak in light fastness, its improvement is an important problem. In addition, along with the recent penetration of digital cameras, the chance to print a photo at home is also increased, and discoloration of a printed image caused by oxidizing gas in the air when the obtained printed article is stored is acknowledged as a problem. Oxidizing gas has a property to react with dye on or in recording paper to discolor or fade a printed image. Among oxidizing gases, ozone gas is considered as the main causative substance to promote the phenomenon of fading an inkjet recorded image. Because the phenomenon of discoloration or fading is characteristics of inkjet image, improvement of ozone gas fastness is also an important problem, as well as improvement of light fastness.
As a coloring matter structure of coloring matter for magenta to be used water-soluble ink for inkjet recording, xanthene-based coloring matter and azo-based coloring matter using H acid is typical. Xanthene-based one is, however, very excellent in hue and vividness but very inferior in light fastness. Some types of azo-based coloring matter using H acid are good in terms of hue and water fastness but inferior in light fastness, gas fastness and vividness. Some magenta dyes of this type has been developed to have excellent vividness and light fastness, but their level of light fastness is still inferior to that of dye of such other hues as cyan dye, yellow dye and the like which are typified by copper phthalocyanine-based coloring matter.
Anthrapyridone-based coloring matter is exemplified as a coloring matter structure of coloring matter for magenta which is excellent in vividness and light fastness (for example, Patent Literatures 1 to 8), however, any type of anthrapyridone-based coloring matter that satisfies all of hue, vividness, light fastness, water fastness, gas fastness and solution stability has not been provided yet.
Patent Literature 1: JP 59-74173 A (Page 1 to 3)
Patent Literature 2: JP 2-16171 A (Page 1 and 5 to 7)
Patent Literature 3: JP 2000-109464 A (Page 1 to 2 and 8 to 12)
Patent Literature 4: JP 2000-169776 A (Page 1 to 2 and 6 to 9)
Patent Literature 5: JP 2000-191660 A (Page 1 to 3 and 11 to 14)
Patent Literature 6: JP 2001-72884 A (Page 1 to 2 and 8 to 11)
Patent Literature 7: JP 2001-139836 A (Page 1 to 2 and 7 to 12)
Patent Literature 8: JP 2003-192930 A (Page 22 and 36 to 37)